Portable refrigerator



FIG. 1 is a front perspective view of a portable refrigerator showing our new design;

FIG. 2 is a front view thereof;

FIG. 3 is a left side view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a top view thereof; and,

FIG. 6 is a bottom view thereof.

The broken lines depicting the remainder of the portable refrigerator form no part of the claimed design. 

CLAIM The ornamental design for a portable refrigerator, as shown and described. 